The present invention relates to systems for underground liquid storage tanks to control spillage during filling of the tank, and in particular to spillage containment vessels for use with such underground tanks.
Underground storage tanks used in the storage of toxic or flammable liquids, such as those used for storage of petroleum products at service stations and the like, normally include a casing or fill pipe that runs from the subsurface tank up to the ground surface. A manhole surrounds the upper end of the casing in order to access the casing and provide clearance for a valve used to connect delivery truck fill hoses to the casing. Although most liquid product delivery trucks are equipped with a shutoff valve that stop liquid flow to the fill hose when a storage tank is full, spillage of product is common when filling such tanks. Spills normally occur due to leakage at the fill pipe-hose coupling or by the discharge of the standing liquid within the truck hose. Even though the truck's shutoff valve halts delivery to the base, the truck hose remains filled with liquid product. When the hose is disconnected from the casing, this remaining liquid runs out onto the ground.
The contamination produced by such liquid storage tank spills results in a substantial health hazard. When toxic or flammable liquids, such as gasoline, diesel fuel or the like are dumped onto the ground, these products may enter the local ground water or otherwise enter into the ecosystem. Even if the spillage is not absorbed into the ground but is drained off into a sewage system, a toxic or explosive atmosphere can be produced within the local sewer system.
The severity of contamination due to underground liquid storage tank spillage is evidenced by the fact that various state and local governments are enacting legislation to require systems for controlling such spills. Although various methods may be utilized on tanks installed in the future, the problem remains with the numerous previously installed underground storage tanks presently in use.
In the spill containment system disclosed in the aforementioned patent, water due to precipitation and/or other liquids and chemicals used to wash pavement often drained into the containment vessel when the vessel was mounted flush with grade. This problem is encountered in the typical gas station installation where, for example, the pavement is often periodically cleaned with a degreasing agent and water. This is undesirable because it lowers the capacity of the containment system to absorb spills and it contaminates the liquids spilled therein with water. The latter problem makes recovery of the liquid spilled for useful purposes quite difficult.